MONDAY, June 22, 2015 (HealthDay News) -- Another study suggests that smartphones should be kept a safe distance from implanted cardiac devices like pacemakers and defibrillators, in the rare chance that signaling "interference" occurs.

"Nearly everyone uses smartphones and there is the possibility of interference with a cardiac device if you come too close," study senior author Christof Kolb, prior head of electrophysiology at the German Heart Centre, said in a news release from the European Society of Cardiology (ESC).

This doesn't mean that people with implanted cardiac devices need to toss their phones away, however.

"Patients with a cardiac device can use a smartphone," Kolb said. "But they should not place it directly over the cardiac device. That means not storing it in a pocket above the cardiac device. They should also hold their smartphone to the ear opposite to the side of the device implant."

One expert in the United States agreed.

"There is no need for patients to be alarmed," said Dr. Marie-Noelle Langan, who directs electrophysiology at Icahn School of Medicine at Mount Sinai in New York City.

"The researchers showed that the potential impact of these devices is quite small," she said.

As the European researchers explained, pacemakers might "misinterpret" electromagnetic interference (EMI) emanating from nearby smartphones as a cardiac signal, which could cause them to stop working.

Although this pause in function is only brief, it could cause people to faint, the researchers said. Meanwhile, an implanted cardiac device might also misinterpret interference from smartphones as a "life-threatening," abnormal heart rhythm and deliver the patient a painful shock.

Currently, the U.S. Food and Drug Administration already recommends that cellphones be kept at least five to seven inches away from an implanted cardiac device. But the study team noted that these guidelines are based on research that's a decade old -- before the advent of smartphones. Mobile network standards have also changed in the last decade, Kolb's team said.

In the new study, the researchers tracked the effects of today's smartphones on more than 300 patients with an implanted cardiac device.

Participants were exposed to the electromagnetic field of three common smartphones: the Samsung Galaxy 3; Nokia Lumia; and HTC One XL. These phones were placed on the patients' skin directly above their heart device.

After being connected to a radio communication tester that functions like a mobile network station, the researchers analyzed how activities such as connecting calls, ringing, talking and hanging up all affected the cardiac devices.

These actions were performed at the maximum frequency known to cause interference, Kolb's group explained.

Meanwhile, electrocardiograms of each person's heart function was recorded continuously and monitored for any signs of a problem.

"From earlier studies we know that the most vulnerable phases of a call are ringing and connecting to the network, not talking, so it was important to analyze these separately," study lead author Dr. Carsten Lennerz, a cardiology resident at the German Heart Centre in Munich, said in the ESC news release.

After conducting more than 3,400 tests on EMI, the study showed that only one of the patients was affected by interference caused by smartphones. This person had an MRI-compatible implanted defibrillator, which misinterpreted electromagnetic waves from the Nokia and HTC smartphones.

The new findings suggest that "interference between smartphones and cardiac devices is uncommon," Lennerz said. However, it "can occur, so the current recommendations on keeping a safe distance should be upheld."

Another expert agreed. "The risk of interaction between today's smartphones and implanted cardiac rhythm devices is exceedingly rare," said Dr. Nicholas Skipitaris, director of cardiac electrophysiology at Lenox Hill Hospital in New York City.

Limiting exposure to high-voltage power lines over bike routes and walking paths and in utility substations is also important to help implanted-device wearers stay safe, a separate study found.

"High electric fields may interfere with the normal functioning of cardiac devices, leading to the withholding of appropriate therapy (anti-bradycardia pacing, for example) or to the delivery of inappropriate shocks," Dr. Katia Dyrda, a cardiologist at the Montreal Heart Institute in Canada, said in an ESC news release.

"There is a lot of interest in using the areas under power lines as bicycle paths or hiking trails because it's essentially free space," she noted. "But patients and the medical community want to understand the risks. There are no recommendations from device manufacturers about power lines or higher electric fields."

In that study, Dryda's team exposed 40 cardiac devices -- including pacemakers and implanted defibrillators -- from five different manufacturers to electric fields up in a high-voltage laboratory.

The heart devices were mounted in a saline water tank at roughly the height of a person's chest.

"There is no significant concern for patients with pacemakers programmed in the usual configuration," said Dyrda. "For the minority of patients with devices in [what's known as] unipolar mode or with very sensitive settings, counseling should be given at implantation or at medical follow-up."

Patients with an implanted cardiac device do not need to avoid crossing under high-voltage power lines, but standing directly under them isn't a good idea. Moreover, it's best to cross under these power lines near the poles that hold them up, since the lines are higher at those points, which minimizes exposure to the electric field, the study's authors advised.

This recommendation doesn't apply to lines that power homes, since the electric field they generate is much lower, the researchers said.

"Patients ask us if they should avoid driving on roads that cross under high-voltage power lines. The answer is no," said Dyrda. "If you're in a vehicle you are always protected, because your car acts as a [protective] cage and shields you automatically."

The study's findings were scheduled to be presented Monday at the joint meeting of the European Heart Rhythm Association of the European Society of Cardiology and Cardiostim in Milan, Italy. Research presented at medical meetings is typically considered preliminary until published in a peer-reviewed journal.